1. Field of the Invention
The present invention relates to a piston type compressor. More specifically, the invention relates to a gas suction structure in a piston type compressor capable of efficiently compressing gas.
2. Description of the Related Art
Piston type compressors are generally used for air-conditioning passenger compartments in vehicles. In the typical compressor, a swash plate is supported on a drive shaft, and a piston is disposed in each cylinder bore a plurality of which are formed around the drive shaft. The rotation of the drive shaft is converted to reciprocating movement of each piston between a top dead center and a bottom dead center in each cylinder bore by the swash plate. With the reciprocating piston, refrigerant gas is sucked from a suction chamber and compressed in a compression chamber of the cylinder bore. Subsequently, the compressed gas is discharged to a discharge chamber.
A piston type compressor having a flapper type suction valve is known. This suction valve selectively opens and closes a suction port defined between each compression chamber and the suction chamber. In this compressor, the refrigerant gas in the suction chamber flows through the suction port, forces the suction valve open, and enters the cylinder bore when the piston is driven in a suction stroke from the top dead center to the bottom dead center. The suction valve closes the suction port when the piston is driven in a compression and discharge stroke from the bottom dead center to the top dead center. The compressed gas in the compression chamber is discharged to the discharge chamber through a discharge port.
The flapper type suction valve is normally closed. Therefore, in order to open the suction port, it is necessary to flex the suction valve against an elastic resistance. For this reason, unless a pressure difference between the compression chamber and the suction chamber is sufficient to overcome the elastic resistance, the suction valve is not opened. As a result, the timing at which the suction port is opened by the suction valve (hereinafter referred to as an open-timing) is delayed. Moreover, when the suction port is closed by the suction valve, the lubricating oil contained in the refrigerant gas adheres to the suction valve and the surrounding surface of the suction port that the suction valve contacts. This oil increases the adhesive force between the suction valve and the surface contacted by the suction valve. Consequently, the suction valve resists opening, and the open-timing of the suction port by the suction valve is further delayed. Such a delay of the open-timing reduces the amount of refrigerant gas that flows into the compression chamber. In other words, the delay reduces the volumetric efficiency of the compressor.
Japanese Unexamined Patent Publication No. Hei 5-231310 discloses a piston type compressor using a rotary valve instead of a flapper type suction valve. In this compressor, the rotary valve is used to improve the volumetric efficiency. The rotary valve is coupled to one end of a drive shaft so that it rotates together with the drive shaft and is located in a valve chamber formed in the cylinder block. Also, the rotary valve is provided with a suction passage, which has an inlet communicating with a suction chamber and an outlet open to the outer peripheral surface of the rotary valve. A suction port is formed between the valve chamber and the compression chamber of each cylinder bore. As the rotary valve is rotated, the outlet of the suction passage is connected in sequence with the suction ports of the compression chambers where a piston is in its suction stroke. As a result, the refrigerant gas within the suction chamber flows into the compression chamber through the suction passage and the suction port. Thus, in the compressor using the rotary valve, there is no need to push and open a flapper type suction valve when the refrigerant gas flows into the compression chamber from the suction chamber. Thus, the refrigerant gas is efficiently introduced into the compression chamber, avoiding a reduction in the volumetric efficiency.
However, if the seal between the outer peripheral surface of the rotary valve and the inner peripheral surface of the valve chamber retaining the rotary valve is poor, the refrigerant gas within the compression chamber where the piston is in the compression or discharge stroke will leak from between the outer peripheral surface of the rotary valve and the inner peripheral surface of the valve chamber through the suction port. In such a case, the volumetric efficiency will be reduced and thus the compressor will not run as efficiently. The seal between the outer peripheral surface of the rotary valve and the inner peripheral surface of the valve chamber depends only on the size of the clearance therebetween. Maintaining the size of this clearance to an appropriate size is very troublesome. In other words, it is very difficult to machine the rotary valve and the valve chamber such that the rotary valve rotates smoothly within the valve chamber while a minimal clearance is maintained to prevent refrigerant gas from leaking from between the peripheral surfaces. Moreover, when an external force, for example, acts on the compressor and the cylinder block is deformed, the clearance between the outer surface of the rotary valve and the inner surface of the valve chamber becomes larger at some locations and the seal therebetween is corrupted.